Python3.X 线程中信号量的使用方法示例_Python

前言

最近在学习python，发现了解线程信号量的基础知识，对深入理解python的线程会大有帮助。所以本文将给大家介绍Python3.X线程中信号量的使用方法，下面话不多说，来一起看看详细的介绍：

方法示例

线程中，信号量主要是用来维持有限的资源，使得在一定时间使用该资源的线程只有指定的数量

									# -*- coding:utf-8 -*-

									""" Created by FizLin on 2017/07/23/-下午10:59

									 mail: https://github.com/Fiz1994

									 信号量

									 maxconnections = 5

									...

									pool_sema = BoundedSemaphore(value=maxconnections)

									Once spawned, worker threads call the semaphore's acquire and release methods when they need to connect to the server:

									pool_sema.acquire()

									conn = connectdb()

									... use connection ...

									conn.close()

									pool_sema.release()

									"""

									import threading

									import time

									import random

									sites = ["https://www.baidu.com/", "https://github.com/Fiz1994", "https://stackoverflow.com/",

									   "https://www.sogou.com/",

									   "http://english.sogou.com/?b_o_e=1&ie=utf8&fr=common_index_nav&query="] * 20

									sites_index = 0

									maxconnections = 2

									pool_sema = threading.BoundedSemaphore(value=maxconnections)

									def test():

									 with pool_sema:

									  global sites_index, sites

									  url = str(sites[sites_index])

									  k = random.randint(10, 20)

									  print("爬去： " + url + " 需要时间 : " + str(k))

									  sites_index += 1

									  # print(url)

									  time.sleep(k)

									  print('退出 ', url)

									for i in range(100):

									 threading.Thread(target=test).start()